Control of autoignition timing in a hcci engine

Abstract

Method and system embody a valve timing strategy to control the autoignition timing of a four stroke internal combustion engine (10) operated in an HCCI mode at different engine operating conditions such as different engine speed and torque. A particular valve timing strategy varies lift timing of the intake valve (20) relative to the exhaust valve (28), or vice versa, and relative to top dead center in response to a change in engine torque, for example, to vary amount of trapped residual burned gas in the combustion chamber (12) flowing to an intake or exhaust port (16,18) and back to the combustion chamber during which the residual gas is cooled. Control of the flow of residual gas between the combustion chamber and intake or exhaust port and thus its temperature by the valve timing strategy, in turn, is used to control the temperature of the fresh air/residual gas/fuel mixture in the combustion chamber (12) and thus autoignition timing in response to a change in engine torque.

Description

BACKGROUND OF INVENTION[0001] 1. Field of the Invention[0002] This invention relates to methods and systems for controlling autoignition timing of an internal combustion engine operated in a homogeneous-charge compression-ignition mode.[0003] 2. Background Information[0004] A conventional gasoline-fueled internal combustion engine employs spark ignition where the fuel and air are premixed and a spark initiates a flame that propagates through the fuel / air mixture in the combustion chamber. The other common type of internal combustion engine employs compression ignition where the fuel and air are purposely kept separate until shortly before top dead center in the engine when the temperature of the air in the combustion chamber is high due to the compression. The fuel then is quickly injected into the combustion chamber as a very fine mist, which partially mixes with the air and autoignites in the combustion chamber. The timing of the fuel injection timing thus controls the autoignitio...

AI Technical Summary

Benefits of technology

0012] The present invention provides a method and system embodying a particular valve timing strategy to control the autoignition timing of a four stroke internal combustion engine operated in the HCCI mode at different engine operating conditions such as at different operator (driver) demanded engine torques. A particular valve timing strategy varies lift timing of the intake valve relative to the exhaust valve, or vice versa, and relative to top dead center in response to a change in operator demanded engine torque, for example, to vary amou...

Problems solved by technology

Control of autoignition timing in an HCCI engine is more difficult than in a diesel engine, which controls fuel injection timing to control autoignition timing.

For example, at higher torque, autoignition timing tends to advance, resulting in the increase in heat transfer losses, NO.sub.x emissions, and combustion noise.

At lower engine torque, autoignition timing tends to be retarded, resulting in an increase of CO emissions and lower combustion efficiency.

However, use of negative valve overlap as a...

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